What Do You See?
Message of the Day: Informed forest management decisions
need information about current and projected conditions
FOR 274: Forest Measurements and Inventory
Growth, Yield and Biomass
• Overview
• Growth Percentage
• Stand Growth
• Tree and Stand Biomass
• Allometrics
• Modeling Growth and Yield
Husch, Beers and Kershaw pp250-257,
chapters 15 & 16
Growth and Yield: Overview
Growth: biological phenomenon of
increase in size with time
Increment: quantitative increase in size in
a specified time interval due to growth
Yield: the total amount (of timber)
available for harvest
Growth and Yield: Overview
Current annual increment: growth within
the past year
Periodic annual Increment: average
growth of a series of years (5 or 10)
Mean annual increment: Current
(cumulative) size divided by the age
Growth and Yield: Overview
Factors affecting growth include:
- genetics
- climatic factors (temp, precip, wind, etc)
- soil factors (moisture, ph, etc)
- topography (slope, elevation, aspect)
- competition (influence of other trees)
Growth and Yield: Overview
To evaluate the usefulness of different
treatment options we often use “growth
and yield models” to forecast the dynamics
of a stand.
Stand dynamics: Growth, mortality,
reproduction, and other stand changes
Growth and yield models produce stand
estimates (basal area, volume, trees per
acre, etc)
Growth and Yield: Overview
Growth Curve: Size plotted against age
Sizes Include:
• Heights
• Volumes
• Diameter
• Weight
Growth and Yield: Overview
Growth Curve: S- (or sigmoid) shaped and
shows cumulative growth at any age
Height
Age
Growth and Yield: Overview
Rate of Growth Curve: Rapid growth in
youth with decreasing rate as tree matures
Rate
Age
Growth and Yield: Overview
Current and mean annual growth curves:
DBH
Growth
Age
Growth and Yield: Growth Percentage
A measure of the average rate of change
in size or volume over a given time interval
Growth percent = 100 * (V2-V1)/(N*V1)
V1 = Volume or size at start
V2 = Volume or size at end
N = number of years
This measure is analogous to interest
rates as found in economics
Stand Growth: Overview
The fundamental components of stand
growth are:
• Accretion – growth of all the trees as
measured at the start of the growth period
• Mortality – Volume of trees initially
measured that died and not utilized
• Ingrowth – Volume of trees grown after
start of the growth period (e.g., seedlings)
Stand Growth: Overview
The fundamental components of stand
growth are:
• Gross Growth – change in total volume
of a stand (including mortality)
• Net Growth – excluding mortality
Production = Net Growth + Ingrowth
Stand Growth: Overview
When considering ecosystems we use the following terms:
• Gross primary productivity (GPP) – total amount of CO2 fixed by a
plant (or stand of plants) due to photosynthesis
• Net primary productivity (NPP) – net amount of CO2 fixed by the
plant after respiration is subtracted from GPP
NPP = GPP - R
• Net ecosystem productivity (NEP) – the net primary production
after all respiration from plants, hetertophs, and decomposes are
included
NEP = GPP – (Rp + Rh + Rd)
NEP is of great interest to people trying to understand the global
carbon budget
Stand Growth: Stand Diameter Distributions
Diameter distributions are required to:
- Construct stand tables
- Estimate stand volume form a stand with
mean DBH and mean height
These distributions are essential components
for forest growth models such as FVS
Stand Growth: Stand Diameter Distributions
Young even-aged stands (before thinning):
Typically uni-modal and approximated by a
normal distribution:
Young Even-Aged Stand
25
20
15
10
5
0
8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
DBH (cm)
Stand Growth: Stand Diameter Distributions
As stands age, mortality and thinning cause
the distributions to become skewed:
Thinned from Below + Mortality
25
20
15
10
5
0
8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
DBH (cm)
Stand Growth: Stand Diameter Distributions
In natural resources we often seek to describe the lifetime of
large numbers under stress: Weibull Distributions
Stand Growth: Stand Table Prediction
Growth projections according to DBH class:
- Develop stand table by DBH class
- Determine past growth via corers or past
inventories
Stand Growth: Stand Table Prediction
Growth projections according to DBH class:
- Apply past diameter growths to current stand
table and estimate mortality and ingrowth
- Periodic stand growth = Volume of future
stand - Volume of present stand
Stand Growth: Producing Future Stand Tables
Need to account for “upward movement”
of trees into higher DBH brackets
Growth-index Ratio = Diameter Growth /
DBH increment = 2.2 / 2 = 1.10
What This Means: 100% of the trees move up 1 DBH bracket
and 10% move up two DBH brackets!
Stand Growth: Producing Future Stand Tables
Based off stem count and DBH the current
and future volumes can be predicted
Stand Growth: Stand Table Prediction
Limitations:
• Method is limited when mortality is high
• Best suited to un-even aged and low
density stands
Tree and Stand Biomass: Overview
Forest Biomass is defined as:
“The total quantity of aboveground live organic floristic matter
expressed as an oven-dry (70°C for 24hrs) weight”
Biomass estimation is important for:
- Plantation forests that are managed for
production of pulpwood or energy
- Quantifying bark etc for products produced
from tannins, etc
- Calculation of carbon pools and stocks for
carbon credit trading
- The study of other biogeochemical cycles
Tree and Stand Biomass: Components
The principal forest biomass components
that we measure include:
• Branches
• Foliage
• Stemwood
• Bark
• Roots
Entire young trees can be measured by felling
but this is expensive and impracticable for
mature tress  sampling methods
Tree and Stand Biomass: Branches and Foliage
Branch biomass is often measured by a 2stage sampling method:
1. Branch diameter is measured 1-2” from
main stem for all branches
2. A sub-sample are used to estimate over
weight. Regression model the used to
estimate total branch weight.
Foliage biomass is often measured by
removing all the needles/leaves from the
tree and calculating the oven-dry weight
on the total or from a 25% sample
Tree and Stand Biomass: Stemwood and Bark
Stemwood biomass is often measured by:
1. Felled volume measured using Smalian’s
formula in 3-10’ sections
2. Dry weight is calculated on cookies
Bark biomass is often clumped into
stemwood calculations or can be achieved
by removing and oven-drying the bark.
Tree and Stand Biomass: Root Biomass
Root biomass is often ignored because
the weight estimation required the
complete excavation of the root system:
It can be achieved using an AirSpade
If you add each estimate together to estimate tree
biomass, remember to add the errors correctly
Allometrics: What is it?
Most people do not have access to the equipment or
personnel to dig up roots. Therefore we use tree allometry.
Tree allometry is the development of quantitative
relationships between “easy to measure”
properties of tree growth and the “difficult to
measure” metric you really need.
Easy to Measure: DBH, Heights, Leaf Area Index
Difficult to Measure: Total standing tree volume,
total carbon content, root carbon
Allometrics: DBH only Relationships
Many types of allometric relationships exist. The simplest type
all have equations of the form:
M = aDb
Where,
M = oven-fry weight of the biomass component (kg), D = DBH
(cm), and a and b are relationship specific parameters
You already know 1 allometric eqn: BA = 0.005454*DBH2 !!!
Allometrics: DBH only Relationships
A review of hundreds of tree allometric relations was
conducted by: Ter-Meikaelian and Korsukhin (1997):
Allometrics: Branch Allometrics
A study by Monserud and Marshall (1999) developed
equations to predict branch and crown area, leaf mass, and
branch wood mass:
Forest Growth Model Systems: FVS
The Forest Vegetation Simulator (FVS) was developed by the
USDA Forest Service and is a widely used to estimate forest
growth in simulated stands.
Advantages: FVS is easy to use and includes modules
that incorporate fire use and insects. Is being adapted to
include spatial data and climate change. Outputs are things
forest managers understand.
http://www.fs.fed.us/fmsc/fvs/software/setup.php
Disadvantages: Predominately based on correlations
between growth and stand variables. Need relationships for
each species. These relationships might change with
changes in climate.
Forest Growth Model Systems: FVS
In timber management, FVS is widely used in the United States
to summarize current and predict future stand conditions.
Other FVS uses include:
- Evaluating management decisions
on stand structure and composition
- Evaluating wildlife habitats
- Evaluating hazard ratings and
estimating timber losses from insects,
diseases, and fire
Forest Growth Model Systems: FVS
Using FVS is very easy.
From file/select locations file
you can view one of the 3
pre-built examples
Numerous management
options can be planned on
specific years: thinning,
harvest, Rx fire, etc
Output is tabular or using the
SVS Movies post processor
you can generate animations
Forest Growth Model Systems: FVS Output
Typical FVS Output Summary:
What happened between 2047 and 2057?
Forest Growth Model Systems: FVS Output
This simulation included:
Rx fire in 2050 under very
dry conditions
Salvage in 2051 of hard and
soft snags
Forest Growth Model Systems: Biome BGC
Biome BGC is a process model that can predict fluxes of
carbon, energy, and water in the vegetation and soil
Advantages: Accounts for a wide range of physical and
biological processes. As such can be applied to any species
in any location; and adaptable to climate changes
Disadvantages: Required measurements more difficult to
obtain. Although models “How” the plants grow – does not
directly provide measures useful to forest managers – such
as available timber for harvest, amount lost in fire, etc
Biome BGC will be covered in detail in FOR 330